Added TestableInput

src/myfasthtml/core/utils.py

@@ -17,3 +17,32 @@ def mount_if_not_exists(app, path: str, sub_app):
   
   if not is_mounted:
     app.mount(path, app=sub_app)
+
+
+def merge_classes(*args):
+  all_elements = []
+  for element in args:
+    if element is None or element == '':
+      continue
+    
+    if isinstance(element, (tuple, list, set)):
+      all_elements.extend(element)
+    
+    elif isinstance(element, dict):
+      if "cls" in element:
+        all_elements.append(element.pop("cls"))
+      elif "class" in element:
+        all_elements.append(element.pop("class"))
+    
+    elif isinstance(element, str):
+      all_elements.append(element)
+    
+    else:
+      raise ValueError(f"Cannot merge {element} of type {type(element)}")
+  
+  if all_elements:
+    # Remove duplicates while preserving order
+    unique_elements = list(dict.fromkeys(all_elements))
+    return " ".join(unique_elements)
+  else:
+    return None